Boilers are the traditional means for supplying energy in many applications despite the fact that they may not be easily matchable to the temperature, pressure, and flow requirements of a particular application. One difficulty in this regard flows from the fact that in a boiler these parameters are not independent, and changes in heat throughput at constant flow, for example, are accompanied by changes in temperature, pressure, or both. In addition, boilers are expensive and complex, and require extensive maintenance. In most instances the boiler feed water requires chemical treatment to retard corrosive wear of the boiler.
Vapor generators of the kind shown in U.S. Pat. No. 4,211,071 and in my copending U.S. patent application Ser. No. 37,029, filed May 8, 1979, represent alternate means for supplying energy, and offer some material advantages over boilers in the way of equipment simplification and reduced maintenance requirements. However, the product stream from a vapor generator contains a relatively high proportion of non-condensibles, which is undesirable in many applications, and in the case of older forms of vapor generators, the non-condensibles include pollutants such as carbon monoxide and unburned hydrocarbons. In addition, when a high pressure stream is required, capital and operating costs for the air compressor stage of a vapor generator are high.
Some energy consuming applications require a liquid product stream which is at a fairly high temperature and a very high pressure. Hot water flooding systems for recoverying oil from reservoirs are one example. Other examples include heating lines for natural gas and petroleum pipelines. On the other hand, other energy consuming applications require a vaporized product from an initially liquefied source, such as propane, while still other applications may require two or more streams at different temperature, pressure, and flow conditions.